The invention relates to improvements in methods of and in apparatus for measuring workpieces, for example, cylindrical workpieces which have axial bores or holes and/or axially extending projections in the form of stubs or the like (hereinafter called stubs).
It is often necessary to machine and/or otherwise finish workpieces with a high, very high or extremely high degree of precision. For example, such precision finished workpieces will be put to use in many types of aircraft, automobiles and/or other categories of vehicles, and at least some of their dimensions must match the desired or optimal dimensions without any or without any presently detectable tolerances. Heretofore known measuring techniques, such as statistical process controlling methods, which have been developed by scientific and industrial establishments are not entirely satisfactory because they are not sufficiently versatile. One of presently known methods involves statistical control of wear upon tools which are subject to gradual wear and are used in many branches of the processing industries. One of the problems which cannot be adequately solved by resorting to presently known techniques is attributable to the continuously increasing utilization of hot- or cold-formed, cast, injection molded, extruded and similarly produced parts. Such mass-producing methods are becoming increasingly popular because they entail considerable savings in material, energy and man hours. On the other hand, extruded, cast, molded or similarly produced parts must be subjected to material removing secondary or finishing treatments if their dimensions are to match the prescribed or desired optimal dimensions. The secondary treatment often involves engagement of successive workpieces by a chuck or the like. The material which is removed from a workpiece, while the workpiece is held by a chuck or a like tool, is often in the form of shavings, dust or other minute particles which float in the air at the material removing station and are likely to penetrate between a workpiece and the chuck to thus affect the accuracy at which a workpiece is being held during removal of material therefrom. A workpiece is further likely to be improperly held by a chuck for any one of several other unforeseen reasons. All this results in the production of a number of defective objects which cannot be readily detected or cannot be detected at all, for example, if the detection of defective or presumably defective objects is dependent on statistical determination of wear upon the material removing tool or tools. The only presently available solution is to monitor each of a short or long series of finished objects or products in a time-consuming operation by resorting to complex and expensive testing equipment. For example, such equipment should be capable of detecting products which are defective due to improper engagement by a chuck because their inner diameter and/or their outer diameter departs from a required value, because their internal surfaces are not concentric with their external surfaces, because the end faces of a solid cylindrical, frustoconical, frustopyramidal, sleeve-like or ring-shaped product are not exactly parallel to each other and/or because the central axes of the products are not exactly normal to their end faces. The just outlined measurements contribute significantly to the cost of such products as well as to the cost of instruments, machines, apparatus and/or other devices in which the products are put to use.
Numerous presently utilized measuring apparatus are designed to carry out statical measurements in accordance with the same principle as manual measurements on measuring tables or measuring stands. Such apparatus employ various work transporting, depositing or positioning and holding or clamping instrumental devices. Particularly the holding or clamping instrumental devices are apt to interfere with the measurements. Reference may be had, for example, to German patent application No. 34 17 741 of Krempel et al. (published Nov. 14, 1985) which discloses a method of and an apparatus for measuring and/or transferring workpieces from a position of readiness to a position for treatment, particularly in a lathe or in a machining center. The measuring unit includes a sensor which can be moved against a workpiece while the workpiece rests on a measuring table. The published patent application of Krempel et al. further proposes to replace the sensor with a clamping or gripping device which is to be used for transfer of workpieces from the positions of readiness to the positions for treatment.
German patent application No. 37 38 165 of Badtke et al. (published May 24, 1989) discloses a work transferring apparatus which employs a lower work carrier and an upper work carrier. The upper work carrier has claws which can engage a workpiece while the latter is supported by the lower work carrier. Once the workpiece is transferred onto the upper work carrier, it is held against rotation relative to the upper carrier. The apparatus of Badtke et al. is not designed to perform measurements upon and/or to facilitate measurement of workpieces on the upper and/or lower carrier.
German Pat. No. 36 13 027 to Weiss (published Sep. 17, 1987) discloses controlled removal and return movement of cylindrical and like workpieces. More particularly, the patent to Weiss discloses a method of fixedly mounting a workpiece in a chuck with assistance from a clamping mandrel. The patentee desires to avoid jamming of the mandrel in the axial bore of the workpiece. To this end, the patentee employs a work clamping device which secures the workpiece to the chuck during extraction of the mandrel. Once the mandrel is extracted, the clamping device is ready to be disengaged from the chuck but not from the workpiece, and the clamping device is thereupon manipulated to separate the workpiece from the chuck.
Presently known measuring apparatus are not suited for dynamic measurement of various parameters of precision finished workpieces, such as the exact contour of a cylindrical peripheral surface, the concentricity or absence of concentricity of the peripheral surface with an internal surface, the inclination of end faces of a ring-shaped, cylindrical or like workpiece relative to each other, the inclination of such end faces relative to the rotational axis of the workpiece and/or the eccentricity or absence of eccentricity of the peripheral surface relative to the axis of rotation. In most instances, dynamic measurement of cylindrical, ring-shaped or like workpieces involves the utilization of mechanical centering devices which must be provided in addition to the work clamping and/or shifting and/or rotating or indexing means. Many conventional measuring apparatus employ turntables with work clamping devices thereon. This interferes with the monitoring of certain parameters of a workpiece on the turntable. Still further, the versatility of presently known measuring apparatus, particularly for dynamic measurement of cylindrical or like workpieces, is unsatisfactory, i.e., it is necessary to design a different measuring apparatus for each of a large number of various workpieces which must be monitored in order to ascertain whether or not their dimensions and/or other parameters match those of an ideal workpiece. The need for a number of specially designed measuring apparatus contributes significantly to the cost of the workpieces and of the machines, apparatus and/or other devices which must employ precision finished parts.